Alarm device using infrared emission for detection and warning of heat build-up

ABSTRACT

An alarm device for checking the temperature of objects placed within a shielded enclosure comprises alarm means and a unit for detecting infrared radiation including a detector which is fitted with a filtering and focusing optical system. At least one orientable mirror is placed on the one hand at one end of a rotatable cylindrical sleeve which extends through the enclosure wall and to which said mirror is attached and on the other hand symmetrically with the detector with respect to a stationary mirror, the mirrors being located in optically opposite relation within the sleeve. The orientable mirror is mounted on the sleeve and capable of pivoting about two axes which are located at right angles to each other and one of which is the axis of said sleeve. The pivotal movements correspond to trajectories of detected surfaces having the shape of a hyperbola or of a hyperbolic envelope.

lJite States atent [1 1 .iamet et al.

111 3,7d9328 1 July 31,1973

ALARM DEVICE USING INFRARED EMISSION FOR DETECTION AND WARNING OF HEATBUILD-UP Inventors: Jean Jamet, 24, rue Esquirol, 75 Paris; LouisPonthus, 21, avenue Jean Jaures, 69 Lyon, both of France Filed: June 8,1971 Appl. No.: 150,976

Foreign Application Priority Data June 12, I970 France ..702l686 US. Cl..250/347, 73/355 R Int. Cl. G0lt l/l6 Field of Search 250/833 H, 71.5S;

References Cited UNITED STATES PATENTS Primary ExaminerJames W. LawrenceAssistant ExaminerDavis L. Willis AnorneyCameron, Kerkam & Sutton [57]ABSTRACT An alarm device for checking the temperature of objects placedwithin a shielded enclosure comprises alarm means and a unit fordetecting infrared radiation including a detector which is fitted with afiltering and focusing optical system. At least one orientable mirror isplaced on the one hand at one end of a rotatable cylindrical sleevewhich extends through the enclosure wall and to which said mirror isattached and on the other hand symmetrically with the detector withrespect to a stationary mirror, the mirrors being located in opticallyopposite relation within the sleeve. The orientable mirror is mounted onthe sleeve and capable of pivoting about two axes which are located atright angles to each other and one of which is the axis of said sleeve.The pivotal movements correspond to trajectories of detected surfaceshaving the shape of a hyperbola or of a hyperbolic envelope.

5 Claims, 2 Drawing Figures PATENIEU JUL 3 l SHEET 2 OF 2 ALARM DEVICEUSING INFRARED EMISSION FOR DETECTION AND WARNING OF HEAT BUILD-UP Theinvention relates to a device which is sensitive to infrared radiationemitted, for example, by uranium rods within a storage chamber. Thisdevice is intended to detect points of abnormal heat build-up inelements such as uranium rods for the purpose of indicating temperaturerises and triggering a signal which provides a warning in the event ofemission of ionizing radiations which accompany said temperature rises.

The use of this device is not necessarily limited to the nuclear fieldbut can readily be contemplated in other industrial areas of interest.Among these may be mentioned the steel-making industry, the glass-makingindustry (monitoring and local analysis of furnaces, roll ing facilitiesand the like). More generally, the device according to the invention issuitable for use in a large number of cases in which environmentalconditions (such as a high temperature or a high level of radiation) areusually hazardous to conventional devices for detecting heat build-up.

Devices incorporating elements for infrared radiation detection whichare sometimes derived from other industrial fields (temperaturemonitoring of axles of railroad cars, for example) have been proposedand employed for monitoring heat build-up in uranium rods. The detectingelements which are frequently employed in the known devices arethermocouples which are placed in proximity to the rods. Thermocouplesare included in pyrometric assemblies in which evaluation of heatbuild-up is obtained by comparison with the ambient or room temperaturebut are attended by a disadvantage in that they are subjected to theinfluence of this temperature. Moreover, the number of devices which arenecessary in order to obtain information relating to the temperature ofall rods at each instant can readily be imagined.

Moreover, the presence of these detecting devices which are placed infairly close proximity to the rods is only liable to cause hindrancewhen handling these lat ter, the more so as handling operations arecarried out only by remote control by reason of the radioactivity.

Consideration could naturally be given to the possibility of installingthe so-called infrared television cameras of the optical-mechanicalscanning type which would permit infrared monitoring of rods. Apart fromthe fact that they have an optical angular field which is too small forthe application which is contemplated, systems of this type would besubject to a number of disadvantages which tend to exclude their use insuch applications. These disadvantages arise from the fact that theoptical systems are of the glass support type in the case of the mirrorsused for focusing on the detector and would accordingly sufferdegradation under the action of ionizing radiations or of anytemperature rise which might occur.

Furthermore, as has been pointed out by M. .latteau and P. Wurtz in ActaElectronica 1969 (Vol. 12 No. l and 4), the detectors employed in thesecameras operate at a low temperature respectively of 30 and 77 K in thecase of Ge (Hg) and In Sb photovoltaic cells, thereby entailing the needto introduce a liquid mixture of helium-neon or of nitrogen within thestorage room. This is an operational limitation of the apparatus whichappears to be ill-suited to its intended function of continuousmonitoring. Moreover, the preamplifier which follows the detector mustalways be connected to this latter by means of short leads for reasonsof protection against spurious signals. In consequence, the preamplifiercannot be mounted outside the storage room, with the result that theelectronic components with which it is constructed would be subjected toionizing radiations and subsequent degradation.

The device in accordance with the invention for detecting abnormal heatbuild-up satisfies practical re quirements much more effectively thanthe devices which have been cited in the foregoing: this device isinsensitive to ambient temperature, to parasitic radiations (of solarorigin in particular) as well as being suited to detection of hot pointseven in an atmosphere of ionizing radiations or of high temperature; thedevice does not take up any space at the level of the rods, producesinformation relating to all the rods and locates any temperature risewith respect to the storage floor; moreover, the operation andsensitivity of the device are such that the detector with which thislatter is fitted does not call for the use of a cooling fluid.

More precisely, the invention proposes an alarm device for checking thetemperature of objects placed within an enclosure which is fitted withisolating means, comprising a unit for detecting infrared radiation andalarm means, said unit being provided with an infrared detector which isfitted with a filtering and focusing optical system, characterized inthat at least one orientable mirror is placed on the one hand at one endof a rotatable cylindrical sleeve which extends through the enclosurewall and to which said mirror is attached and on the other handsymmetrically with said detector with respect to a stationary mirror,said mirrors being located in optically opposite relation within saidsleeve and said orientable mirror being pivotally mounted on said sleeveand adapted to be driven in two movements of rotation about two axeswhich are located at right angles to each other and one of which is theaxis of said sleeve, said movements of rotation being such as tocorrespond to trajectories of detected surface having the shape of ahyperbola or of a hyperbolic envelope.

Apart from this main arrangement, the invention consists in a number ofother arrangements which can be adopted either separately or preferablyat the same time. The invention is directed to a number of modes ofconstruction and application (especially detection of abnormal heatbuild-up in uranium rods) and by way of novel industrial products to thedetection devices for the practical application of the foregoingarrangements, the elements and special tools which are employed in orderto carry said arrangementsinto effect as well as the stationary andmovable assemblies embodying devices of this type.

The invention applies particularly to a device for detecting abnormalheat build-up in uranium rods whichv hand to orient the optical systemwithin the storage room and on the other hand to process the data whichare collected at the output of the detector element in the event oftriggering of an alarm.

means for providing protection against radiations which might escape viathe passage of the device through the walls of the storage room.

A better understanding of the invention will be obtained from thedescription of one embodiment which is given by way of non-limitativeexample in conjunction with the accompanying drawings, in which:

FIG. 1 is a theoretical diagram showing the endoscope panning pattern;

FIG. 2 is a diagrammatic profile view of the device.

in PK]. 1, the plane XOY is the floor of the storage room. The mirrors Mand M constitute the endoscope. The mirror M is capable of moving abouttwo perpendicular axes; one axis which is located parallel to YYconstitutes the optical axis of the endoscope whilst the other isparallel to XX. The mirror M is stationary and inclined at an angle of45 to the vertical plane XOZ which is parallel to one of the verticalwalls of the storage room of parallelepipedal shape through which theendoscope passes. Said mirror serves to reflect the infrared radiationto the lens M for focusing on the detector and also performs thefunction of infrared filter. Taking into account a pupil which limitsthe field at M for example, a correspondence is thus established betweena surface area S of the radiation emitting room and the surface area Sof the detector to which said radiation is applied.

The traces described on the ground by S as a result of the alternatemovements of the above-mentioned mirror are hypcrbolas which arerelatively displaced in orthogonal affinities. The distance a and bindicate the dimensions of said hyperbolas.

One form of construction of the endoscope which is placed through aconcrete wall 1 is shown in FIG. 2 The endoscope comprises a tubularsleeve 2 which is capable of pivoting about a horizontal axis within twobearings as well as sintered bronze supports 3 and 4 which permitoperation without lubrication since any organic substance could bedamaged as a result of gamma radiation. Movement ofthe sleeve iscontrolled by means of a cam 5. The mirror 6 is capable of pivotalmovement about the pin 7 by means of the link-rod system 8 which iscontrolled by the cam 9, the mirror 6 corresponding to mirror M inFIG. 1. The second mirror 10 of the endoscope is stationary and reflectsthe flux to the optical unit 11 for focusing and detection, the mirror10 corresponding to mirror M in FIG. 1. A mirror 12 or so-called copyingmirror is coupled mechanically to the mirror 6 by means oflink-rodsystems 7 and I3 and is capable of pivoting about the pin 14. An angleof 90 is made continuously between the plane of said copying mirror andthe plane of the mirror 6. Th mirror 12 produces an image of the lamp 15or so-called copying lamp on a matrix 16 which is covered withphotoelectric CdS detectors each corresponding to one of the uraniumrods. In the event of triggering of an alarm, the correspondence whichis thus ensured between a uranium rod 17 and a CdS cell 18 serves tolocalize a state of heat build-up.

The restoring springs 19, 20 and 21 form part of the mechanical linkageswhich have been described above.

The mirrors 6, l0, 12 are formed of stainless steel which cannot beattacked by radiations and may be cooled ifnecessary by means of aliquid coolant which flows through ducts in thermal contact with themetallic supports of the mirrors.

The sleeve of the endoscope is also formed of stainless steel ofsubstantial thickness in order to form a shield against radiationsemanating from the storage room. Said sleeve is therefore intended atthe same time to perform a shielding function by virtue of a suitablechoice of the metal of which it is formed. Moreover, the endoscopecomprises a lead sheath at the end nearest the storage room.

The cams which control the two movements of rotation of the movablemirror 6 are in turn controlled by hydraulic jacks which are supplied bytwo separate hydraulic circuits each provided with a pump in order toprevent any jerky operation in the rotational motion of the mirror. Saidcircuits are fitted with flow-regulating devices which serve to adjustthe speeds of rotation about each pivot-pin. One of the movements ofrotation can therefore be carried out at a higher speed than the other.This possibility has an advantage: in fact, in order to ensure that allthe rods may be entirely covered at least once per scan, it is onlypossible to contemplate transverse scanning of rods; in the case of agiven rod-storage room in which the rods are placed on the floor in thelengthwise direction of the room. it is therefore possible tocontemplate an installation of the endoscope through a wall which isparallel to a plane passing through XOZ or to YOZ as shown in FIG. 1; inthe case of the plane XOZ, the fastest movement will be that whichcorresponds to the traces of S in the shape of a hyperbola; in the easeof the plane YOZ, the movement ofS will be a kind of sinusoid which isslowly enveloped by a hyperbola of the type mentioned above; the devicethus exhibits appreciable ease of adaptation to the conditions which aredictated by industrial problems.

The constructional design described in the foregoing is employed in thecase of rods located within a room having a width of 3 meters and alength of 6 meters. The height of installation of the endoscope is 2meters and this latter is installed at the center of one of the verticalwalls of greatest length.

The energy problem of detection can be stated as follows: the uraniumrods are sheathed in hollow magnesium radiators each provided with fourmain cooling fins in the lengthwise direction and between these firstfins with a plurality of secondary herringbone fins which are joined tothe main fins. Heat dissipation resulting from these fins is such thatheat build-up at one point of the uranium rod results in approximatelyonehalf of said heat build-up at distances of 2.5 to 3 cm around the hotpoint. in consequence, if the heat buildup of uranium attains 300 C, itwill only attain 150 at a distance of 3 cm. Taking these results intoaccount and in order to set the alarm at 300 C, the detection thresholdhas been set at 150 C and the scanning pitch has been established at amaximum value of 5 cm.

The surface area S which is in optical correspondence with the detectorcell is chosen so as to be as large as possible and remains containedwithin a circle of 7 cm as imposed by the dimensions of the radiator.The detected light beam is practically constant to within 10 percent inorder to ensure that the energy received by the detector is a functiononly of the luminance of the rods. Said rods in any case behavevirtually as a black body and in accordance with Lamberts law up toangles of inclination greater than with respect to the normal. Thevariation of the angle of inclination of the beam derived from S andfalling on M therefore does not have any contributory function in thetriggering of the alarm system.

In the device in accordance with the invention, the infrared filterwhich is employed is a germanium lens of type n which transmits infraredradiation within the range of 2 m to 17 p.111. it would have beenpossible to employ infrared filters of a different type such as leadsulphide or indium antimonide. Above 2 pm, the luminance reflected fromthe body under observation which would arise from the presence ofartificial sources is very small compared with the luminance of thermalorigin; the spectral range considered is that of passive observation(refer to Acta Electronica, Vol. 7 Oct. 63 No. 4 page 300); protectionagainst parasitic radiations other than thermal radiations is ensured.

Taking into account the alarm threshold and the thermal emissionproperties of the rod, the conditions of filtering of the optical systemand of the atmosphere of the emitting surface which is chosen, thevariation in flux received by the detector at the time of modulation ofthe optical beam is of the order of l aw in the event of an alarm. Thispower to be detected is very substantial and a large number of detectorsare suitable for this purpose. Only practical reasons lead to a choiceof uncooled receivers. Among these, the semi-conducting thermistorbolometer or the triglycin sulphide pyroelectric bolometer are worthy ofmention since their range of sensitivity extends far into the infraredregion. The first bolometer is relatively slow and can scarcely bemodulated above 100 cps.

On the other hand, the second bolometer mentioned above readily permitsmodulations of approximately 1000 cycles per second with sensitivitiesof 1,000 V/W and a noise power which is equivalent to 7 l0 Wcps" 9;thus, by adopting a detection of synchronous type and a band of l cps,this results in the case of the device according to the invention in aninput alarm signal of 1 mV with a signal/noise ratio of 7 10'.

These values are very high and result in high operational safety andreliability of the alarm system.

The fact that it is possible to modulate at high frequeney securesfreedom from low-frequency drift and protection against parasiticinductions at the mains supply frequency.

What we claim is:

1. An alarm device for checking the temperature of objects within anenclosure wall having isolating means, comprising a unit for detectinginfrared radiation and alarm means therefore, said unit including aninfrared detector having a filtering and focussing optical system, ascanning mirror having two movements passing through axes perpendicularin said enclosure at one end of a rotatable sleeve extending throughsaid enclosure wall, a copying mirror attached to the other end of saidsleeve outside of said enclosure wall, a mechanical linkage between saidmirrors maintaining their reflecting surfaces at relative to each other,a fixed mirror disposed at 45 with respect to the long axis of saidsleeve passing through said scanning and copying mirrors, said fixedmirror reflecting the radiation from said scanning mirror to said unitfor detecting infrared radiation, and photoelectric detecting means fordetecting the movement of said scanning mirror optically linked to saidcopying mirror for localizing the infrared radiation.

2. A device in accordance with claim 1, the two movements of saidscanning mirror tracing trajectories of detected surfaces having theshape of a hyperbola.

3. A device in accordance with claim 1 the two movements of saidscanning mirror being adjustable whereby one movement may be reversedwith respect to the other.

4. A device in accordance with claim 1, said photoelectric detectingmeans including a virtual point lightsource producing a beam projectedonto said copying mirror and reflected onto a photoelectric detectingmatrix swept by said beam.

5. A device in accordance with claim ll, said sleeve being of stainlesssteel forming a part of said isolating means.

UNITED STATES PATENT OFFICE Certificate Patent No. 3,749,928 PatentedJuly 31, 1973 Jean J amet and Louis Ponthus Application having been madeby Jean J amet and Louis Ponthus, the inventors named in the patentabove identified, and Commissariat a lEnergie Atomique, Paris, France,the assignee, for the issuance of a certificate under the provisions ofTitle 35, Section 256, of the United States Code, deleting the name ofJean J amet as a joint inventor, and a showing and proof of factssatisfying the requirements of the said section having been submitted,it is this 2nd day of July 197 4:, certified that the name of the saidJean iamefi is hereby deleted from the said patent as a joint inventorwith the said Louis ont us.

FRED W. SHERLING,

Associate Solicitor.

$22353?" I UNITED STATES PATENT OFFHCEJ CERTIFICATE OF CORREQION PatentNo. ,7 ,92 Dated July 31, 1973 I c Jean Jamet and Louis Ponthue It iscertified that error appears in the aboveuantified patent end that said.Letter's Patent are hereby correctefi ea ehown [76] Inventor: vLouise.Ponthus, 21, avenue Jean Jaures, 69

Lyon of France Signed and sealed this 5th day of November 1974,

(SEAL) Attest:

GIBSON JR. C. MARSHALL DANN Commissioner of Patents McCOY M. AttestingQfficer

1. An alarm device for checking the temperature of objects within anenclosure wall having isolating means, comprising a unit for detectinginfrared radiation and alarm means therefore, said unit including aninfrared detector having a filtering and focussing optical system, ascanning mirror having two movements passing through axes perpendicularin said enclosure at one end of a rotatable sleeve extending throughsaid enclosure wall, a copying mirror attached to the other end of saidsleeve outside of said enclosure wall, a mechanical linkage between saidmirrors maintaining their reflecting surfaces at 90* relative to eachother, a fixed mirror disposed at 45* with respect to the long axis ofsaid sleeve passing through said scanning and copying mirrors, saidfixed mirror reflecting the radiation from said scanning mirror to saidunit for detecting infrared radiation, and photoelectric detecting meansfor detecting the movement of said scanning mirror optically linked tosaid copying mirror for localizing the infrared radiation.
 2. A devicein accordance with claim 1, the two movements of said scanning mirrortracing trajectories of detected surfaces having the shape of ahyperbola.
 3. A device in accordance with claim 1 the two movements ofsaid scanning mirror being adjustable whereby one movement may bereversed with respect to the other.
 4. A device in accordance with claim1, said photoelectric detecting means including a virtual pointlight-source producing a beam projected onto said copying mirror andreflected onto a photoelectric detecting matrix swept by said beam.
 5. Adevice in accordance with claim 1, said sleeve being of stainless steelforming a part of said isolating means.